Traditionally, telecommunications facilities have relied on a commercial power utility as their primary source for electrical power. In the case of a sudden power loss, e.g., a black-out or other disturbance in the commercial power grid, some sort of backup system is necessary to maintain power to the telecommunications equipment.
Most facilities use a diesel generator and an array of batteries as backup power sources. Operationally, if power from the commercial utility is lost, the diesel generator is activated to supply power to the facility. It takes time for the diesel generator to come on line, though. Because of this, the battery array provides power during the time it takes to switch from the utility source to the diesel generated source. If the generator also fails (e.g., if the generator breaks down or runs out of fuel), then the battery array is able to provide power for an additional (but limited) period of time.
With respect to the batteries used, conventional systems use valve-regulated lead-acid (VRLA) batteries. These batteries have limitations. First, VRLA batteries produce harmful and corrosive gases. Thus, they require adequate ventilation. Ventilation is required by Environmental Protection Agency (EPA) standards. Second, VRLAs take up considerable space. This is because they have energy densities which are relatively low. Because of this, users normally have to dedicate large areas in the plant, and perhaps even multiple rooms, just to house them. Other limitations include that VRLAs have limited life spans and require continual maintenance. The life cycle of the VRLA is a slow death in that their charge-holding capacities become reduced over time until the battery has become unable to properly function and must be discarded.